The invention was developed primarily for use with electron bombardment and the deposition of metal ions and their associated oxides, and will be described hereinafter with reference to these applications. However, it will be appreciated that the invention is not limited to these particular fields of use, and is also suitable for vacuum deposition of nitrides and carbides.
Macroparticles are those particles emitted from the cathode with sizes ranging between 0.1 microns up to 10 microns. Without removal of these macroparticles from the plasma the resulting coating is found to be non-uniform and cratered. When a coating is to be applied in a high precision application such as those associated with microelectronic or optical fields, macroparticles are particularly undesirable.
The presence of macroparticles in the plasma prevents prior art arc sources from being effectively able to produce electron beams for heating of associated work pieces. When applied to this manner of operation the macroparticles would partially cover and mark the workpiece making it unsuitable for further coatings.
In conjunction with the above mentioned problem, the presence of macroparticle does not create a favourable environment for the deposition of various coatings, in particular vanadium dioxide. This coating is of considerable interest due to its transition between semiconductor and metallic properties over a small temperature range, but is difficult to produce in the exact atomic proportions required.
In the past, many macroparticle filters have included the use of 90.degree. bending of the plasma by magnetic fields so that the much larger macroparticles would separate from the plasma. However, an extended magnetic field is needed to produce the required bending and confining of the plasma. These prior art devices only accommodate positive ion currents of less than 200 mA for 100 A arcs, and thereby have a very restricted deposition rate and film growth rate.